Node-B scheduling is a process in which a node-B controls uplink transmissions of user equipments (UEs) present in a cell controlled by the node-B when the UEs transmit packets in the uplink. The control by the node-B is in real time. Such control may more efficiently utilize uplink resources and improve cell throughput and capacity.
In a related art node-B scheduling method, the node-B transmits a command for limiting uplink packet transmission power level or transmission data rate of the UEs at each transmission time interval (TTI). This limitation allows rise over thermal (ROT) in the cell to be maintained at an appropriate level.
A UE may be in a soft handover between two or more node-Bs. One of the node-Bs may provide a scheduling command pertaining to the uplink transmission power level or transmission data rate of the UE. The node-B providing the scheduling command is referred to as a scheduling node-B of the UE. Conversely, a node-B in communication with the UE during handover that does not provide a scheduling command pertaining to the UE is referred to as a non-scheduling node-B of the UE.
A UE in soft handover with a node-B and receiving a scheduling command from the scheduling node-B is referred to as a scheduled UE of the node-B. Conversely, a UE in soft handover with a node-B receiving no scheduling command of the node-B is referred to as a non-scheduled UE of the node-B.
A scheduling node-B may be unable to determine interference caused by a scheduled UE to neighboring non-scheduling nodes. Therefore, the scheduling node-B may be unable to account for the interference to the neighboring cells in scheduling the scheduled UE. Therefore, the node-B may be unable to control the interference caused by its scheduled UEs, even in cases of excessive interference.
One proposal for limiting the interference involves a node-B transmitting uplink transmission power level or transmission data rate reduction commands to non-scheduled UEs of the node-B in the downlink. The reduction commands include a ‘Down’ command for reducing the uplink transmission power level or transmission data rate and a ‘None’ command to indicate that no specific operation is required. When the UE receives a Down command from the non-scheduling node-B, the UE reduces its uplink transmission power level or transmission data rate to a specific level, regardless of a scheduling command received from the scheduling node-B. Conversely, when the UE receives a None command indicating no specific operation, the UE increases or decreases its transmission power level or transmission data rate according to a command from the scheduling node-B. The node-B may transmit Down/None commands to individual non-scheduled UEs of the node-B or, alternatively, may broadcast Down/None commands to all non-scheduled UEs of the node-B.
FIG. 1 is a diagram illustrating a related art node-B scheduling method.
Referring to FIG. 1, in a time interval in which a UE receives a None command from its non-scheduling node-B that indicates no specific operation, the UE increases or decreases its uplink transmission power level or transmission data rate according to a command from its scheduling node-B. The non-scheduling node-B transmits a Down command to the UE if the interference to the non-scheduling node-B rises above a certain level as the UE increases the transmission power level or transmission data rate according to the scheduling command from the scheduling node-B.
Upon receiving a Down command from the non-scheduling node-B, the UE decreases the transmission power level or transmission data rate to a specific level, regardless of the scheduling command from the scheduling node-B. If the uplink transmission power level or transmission data rate of the UE drops below the scheduled rate, the scheduling node-B attempts scheduling of the UE to raise the transmission power level or transmission data rate back to a desired level. As a result, the interference to the non-scheduling node-B increases, causing the non-scheduling node-B to retransmit a Down command. As this process repeats, the interference to the non-scheduling node-B repeatedly increases and decreases (e.g., oscillates).
Accordingly, the interference to the non-scheduling node-B may not be maintained at a desired level, causing difficulty for the non-scheduling node-B to perform appropriate scheduling of its scheduled UEs. Furthermore, it may be difficult for each scheduling node-B to properly schedule its UEs, since uplink ROT caused by UEs in soft handover greatly varies.